Patent GB-892514-A (GB)
Title: Improvements relating to control apparatus for turbine-type power plants
IPC: B64C27/14
Filed: 1958-10-21
Abstract: 892,514. Gas turbine plant. UNITED AIRCRAFT CORPORATION. Oct. 21, 1958 [Oct. 23, 1957], No. 33616/58. Class 110 (3). [Also in Group XXIX] Control apparatus for a power plant having a combustion section, and at least one turbine driven by gas produced in the combustion section comprises means for connecting a source of fuel under pressure to the combustion section, means for regulating the flow of fuel from the source to the combustion section, a first-servo mechanism responsive to the speed of said turbine, and fuel flow adjusting means operatively connecting said first-servo mechanism to said fuel flow regulating means to adjust said regulating means in response to changes in turbine speed, wherein said adjusting means includes a second-servo mechanism and, for a given speed change, said adjusting means provides a first change of fuel flow and said second servo-mechanism then operates to modify the operation of the adjusting means to provide a second subsequent change of fuel flow. In an embodiment the turbine type power plant has a first stage turbine which drives the compressor and a second stage turbine that is independent of the first stage turbine and compressor and drives the rotor of the helicopter. Fuel for the combustion section of the power plant enters at 60 through a filter 62 and flows past a throttle valve 66-and shut-off valve 84 to an outlet line 90 and overspeed shut-off valve 96, from whence it passes to the power plant combustion section. The throttle valve 66 is actuated by a servopiston 102 under the influence of a servo-control valve 110, the setting of this valve determining the fluid pressure on the undersurface of the servo-piston 102, fluid being fed into the servocylinder through an orifice 100. The valve member 112 pivots about a fulcrum 118 and is subjected to loading through the rollers 124, the loading varying with compressure discharge pressure, compressor inlet temperature, turbine speed and rotor speed. Follow-up action for the valve 110 is provided through the spring 132. Compressure discharge pressure is passed to the inside of bellows 128 and acts as a downward loading on lever 120, pivoted at its lefthand end. A second bellows 126 is mounted below the lever 120 and is evacuated. The net loading therefore represents compressor discharge pressure absolute. The loading on lever 120 responsive to compressor discharge pressure is transmitted to the valve member 112 through the rollers 124. The speed of the turbine driving the compressor is sensed by a centrifugal governor indicated generally at 198. This governor exerts a force proportional to turbine speed on a lever 200 constituting the valve obturating member of an orifice 206 such that the servo-piston 210 is caused to move axially with variations in speed. Vertical movement of the cam member 196 moved by the servo-piston 210 causes horizontal movement of rod 194 which through lever 142 displaces the rollers 124, thereby varying the loading on servo-valve 110. A similar type of servodevice (Fig. 3, not shown) transmits rotational movement to the cam member 196 in response to compressor inlet temperature, causing longitudinal movement of rod 194 and consequent adjustment of the rollers 124. The speed of the rotor driven by the free turbine is sensed by a centrifugal governor indicated generally at 168. This governor controls a servo-valve 172 associated with a servo-piston 182 such that the position of the piston 182 is at all times proportional to rotor speed. By means of levers 161 and 159 the roller 327 imparts a signal to the left-hand of lever 158 proportional to rotor speed. The lever 158 pivots about an adjustable camoperated pivot 160 which varies with the setting of the power control lever 86 which also controls the shut-off valve 84. With the lever 158 pivoting about cam 160, positioned in proportion to desired speed, the right-hand end of the lever provides a signal proportional to the speed error at any particular instance. This signal acts on lever 148, which pivots at 150, and through lever 144 and bell-crank 146 adjusts the position of rollers 124. In order to avoid excessive hunting when variations in rotor loading occur the system also provides an additional fuel flow signal of limited duration during transient conditions. If the loading on the rotor is increased resulting in a decrease in rotor speed link 162 will move the left-hand end of link 159 in a downward direction causing the link to pivot about 326 and depress the left-hand end of lever 158 thereby calling for an increase in fuel flow. The pivotal movement of link 159 about 326 also causes the lever 330 to pivot about 332 and displace the servo-valve 334, admitting pressure fluid to the undersurface of piston 320. Upward movement of the piston causes the lever 322, pivoted at 324 to impart an additional downward movement of roller 327 and hence an additional fuel flow signal, the magnitude of the signal depending upon the rate of change of the rotor speed. The rate of application of the fuel flow signal may be adjusted by varying the relative location of the points 326, 327. The overspeed shut-off valve is actuated by the servo-piston 182 and shuts down the supply of fuel to the power plant should the rotor speed exceed a pre-delivered figure. Specifications 753,970 and 837,558 are referred to.